This application claims the benefit of Japanese Application 2001-201419, filed Jul. 2, 2001, and Japanese Application 2002-057107, filed Mar. 4, 2002, the entireties of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stacked dielectric filter which constitutes a resonance circuit in a microwave band of several hundreds MHz to several GHz. In particular, the present invention relates to a stacked dielectric filter which makes it possible to effectively miniaturize communications equipment and electronics equipment.
2. Description of the Related Art
In recent years, there has been a strong demand to realize a small-sized and thin high frequency filter to be used for wireless communication equipment. Therefore, it is indispensable to use a stacked dielectric filter.
In general, as shown in FIG. 30, such a stacked dielectric filter, for example, a stacked dielectric filter 400 using a xc2xc wavelength resonator has a plurality of resonant electrodes 402, 404, inner layer ground electrodes 406, 408, 410, 412, and a coupling-adjusting electrode 414. Each of the plurality of resonant electrodes 402, 404 has an end electrically connected to a ground electrode. Each of the inner layer ground electrodes 406, 408, 410, 412 has an end electrically connected to the ground electrode. The inner layer ground electrodes 406, 410 are stacked to sandwich a part of an open end of the resonant electrode 402 and a dielectric layer. The inner layer ground electrodes 408, 412 are stacked to sandwich a part of an open end of the resonant electrode 404 and the dielectric layer. The coupling-adjusting electrode 414 electromagnetically couples the respective resonant electrodes 402, 404.
However, in the stacked dielectric filter 400 as shown in FIG. 30, the ground electric potential is used as the reference electric potential for inputting/outputting a signal of an unbalanced form. Therefore, for example, in order to connect the stacked dielectric filter 400 to a high frequency amplifying circuit of the balanced input type, it is necessary to use a balun (balanced-unbalanced converter) additionally between them. Consequently, a certain limit arises in the miniaturization.
In the above example, the stacked dielectric filter using the xc2xc wavelength resonator is described. Additionally, stacked dielectric filters of the balanced type using xc2xd wavelength resonators have been also suggested (see, for example, Japanese Laid-Open Patent Publication 11-317603, 2000-353904, and 2000-22404).
In each of the stacked dielectric filters of the balanced type, the resonator length is inevitably increased, because the stacked dielectric filter is composed of the xc2xd wavelength resonator. Therefore, such a stacked dielectric filter is disadvantageous to realize a small sized filter.
It is therefore an object of the present invention to provide a stacked dielectric filter of a small size which enables a balanced input/output for connection to a high frequency amplifying circuit or the like.
Another object of the present invention is to provide a stacked dielectric filter in which it is unnecessary to separately insert any circuit for connecting a DC power source to an IC when the IC is connected to an unbalanced-balanced converting section, while reducing the number of parts, suppressing the insertion loss, and miniaturizing the size of electronic devices including the IC.
Still another object of the present invention is to provide a stacked dielectric filter in which it is unnecessary to separately insert any circuit for matching the impedance between an unbalanced-balanced converting section and an IC when the IC is connected to the unbalanced-balanced converting section, and it is possible to reduce the number of parts, while suppressing the insertion loss, and miniaturizing the size of the electronic devices including the IC.
Still another object of the present invention is to provide a stacked dielectric filter which enables an increased degree of flexibility of design.
Still another object of the present invention is to provide a stacked dielectric filter in which it is possible to reduce the electrode area in a filter section, and it is possible to suppress the stray coupling in an unbalanced-balanced converting section.
The present invention provides a stacked dielectric filter comprising a filter section having a plurality of resonators for filtering an unbalanced signal, and at least one unbalanced-balanced converting section having strip lines. The filter section and the unbalanced-balanced converting sections are in a dielectric substrate including a plurality of stacked dielectric layers.
Accordingly, the filter section can be composed of the xc2xc wavelength resonator by which it is advantageous to realize the miniaturization. It is possible to realize compact or small sized devices as compared with stacked dielectric filters of the balanced type composed of xc2xd wavelength resonators.
Further, it is unnecessary to set the characteristic impedance between the filter section and the unbalanced-balanced converting section to have a specified value (for example, 50xcexa9). The characteristic impedance can be arbitrarily determined. Therefore, it is possible to enhance the degree of flexibility of design. Further, the filter section can be easily formed, and it is possible to widen the line width of the strip line of the balun section, because the characteristic impedance can be determined to be low. Therefore, it is possible to reduce the loss in the unbalanced-balanced converting section.
As described above, the present invention provides the stacked dielectric filter of the small size which enables the balanced input/output for connection to the high frequency amplifying circuit or the like.
In the stacked dielectric filter, the plurality of dielectric layers of different materials may be laminated or stacked to provide the dielectric substrate. Preferably, a dielectric constant of the dielectric layer corresponding to the filter section is higher than a dielectric constant of the dielectric layer corresponding tothe unbalanced-balanced converting section.
Accordingly, it is possible to reduce the electrode area in the filter section, and it is possible to suppress the stray coupling in the unbalanced-balanced converting section.
The stacked dielectric filter may be exemplarily constructed as follows. For example, the filter section is formed at an upper portion or a lower portion in a stacking direction of the plurality of dielectric layers of the dielectric substrate, and the unbalanced-balanced converting section is formed at a portion other than the upper portion and the lower portion. In this arrangement, an inner layer ground electrode for isolating the filter section from the unbalanced-balanced converting section can be easily formed between the filter section and the unbalanced-balanced converting section. Thus, it is possible to improve the characteristics.
Alternatively, the filter section may be formed at a left portion or a right portion in a stacking direction of the plurality of dielectric layers of the dielectric substrate, and the unbalanced-balanced converting section may be formed at a portion other than the left portion and the right portion.
Further, ground electrodes may be formed on both principal surfaces of the dielectric substrate, and planes on which resonant electrodes of the plurality of resonators are formed and planes on which the ground electrodes are formed may be parallel to one another. Planes on which input/output terminals of the filter section are formed and planes on which the strip lines of the unbalanced-balanced converting section are formed may be perpendicular to one another.
Alternatively, ground electrodes may be formed on both principal surfaces of the dielectric substrate, and planes on which resonant electrodes of the plurality of resonators are formed and planes on which the ground electrodes are formed may be perpendicular to one another. In this arrangement, planes on which input/output terminals of the filter section are formed and planes on which the strip lines of the unbalanced-balanced converting section are formed may be parallel to one another. The input/output terminals of the filter section and the strip lines can be arranged away from each other. Therefore, it is possible to eliminate any unnecessary interference between the input/output terminals of the filter section and the strip lines of the unbalanced-balanced converting section. Thus, it is possible to improve the characteristics.
Further, the unbalanced-balanced converting section may be connected via a connecting section to an input side and/or an output side of the filter section. In this arrangement, the stacked dielectric filter may further comprise an inner layer ground electrode which is provided in the dielectric substrate and which is connected to a ground electrode, wherein the connecting section is formed separately from the unbalanced-balanced converting section with the inner layer ground electrode interposed therebetween, and the connecting section is electrically connected to an unbalanced input/output section of the unbalanced-balanced converting section. It is preferable that the inner layer ground electrode is formed for at least isolating the filter section from the unbalanced-balanced converting section.
It is preferable that the connecting section has a connecting electrode which is connected to the filter section via a capacitor. If the filter section is directly connected to the unbalanced-balanced converting section, then unnecessary matching issues are caused between the filter section and the unbalanced-balanced converting section in the attenuation region of the bandpass characteristics, and an unnecessary peak is formed in the attenuation region. Accordingly, when the filter section is connected to the unbalanced-balanced converting section via the capacitor as in the present invention, then the phase of the unbalanced-balanced converting section is shifted by the capacitor, and it is possible to suppress the unnecessary matching with respect to the filter section. If the connecting electrode is arranged on the side of the unbalanced-balanced converting section, the connecting electrode may be coupled to the unbalanced-balanced converting section, and the bandpass characteristics may be deteriorated. Therefore, it is preferable that the connecting electrode is arranged on the side of the filter section.
On the other hand, the unbalanced-balanced converting section may comprise a first strip line which is formed on a first principal surface of the dielectric layer and which has a first end constituting an unbalanced input/output section; a second strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to one balanced input/output terminal, and which is connected to a ground electrode at an arbitrary position on the line; and a third strip line which is formed on the first principal surface of the dielectric layer, which has a first end connected to the other balanced input/output terminal, and which is connected to the ground electrode at an arbitrary position on the line.
In this arrangement, the stacked dielectric filter may further comprise an inner layer ground electrode which is provided in the dielectric substrate and which is connected to the ground electrode, wherein second ends of the second and third strip lines are connected to the inner layer ground electrode through via-holes.
Alternatively, when a DC electrode, which is connected to a DC power source, is formed on a surface of the dielectric substrate, the unbalanced-balanced converting section may comprise a first strip line which is formed on a first principal surface of the dielectric layer and which has a first end constituting an unbalanced input/output section; a second strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to one balanced input/output terminal, and which is connected to the DC electrode at an arbitrary position on the line; and a third strip line which is formed on the first principal surface of the dielectric layer, which has a first end connected to the other balanced input/output terminal, and which is connected to the DC electrode at an arbitrary position on the line.
In this arrangement, the stacked dielectric filter may further comprise an inner layer ground electrode which is provided in the dielectric substrate and which is connected to a ground electrode, wherein the second and third strip lines are connected to the DC electrode at respective arbitrary positions on the second and third strip lines through viaholes respectively beyond the inner layer ground electrode. Alternatively, the stacked dielectric filter may further comprise an inner layer DC electrode which is provided in the dielectric substrate and which is connected to the DC electrode, wherein the second and third strip lines are connected to the inner layer DC electrode at respective arbitrary positions on the second and third strip lines through the via-holes respectively.
Explanation will now be made for an exemplary form of use of the stacked dielectric filter. When the stacked dielectric filter is used, an IC is connected to the stacked dielectric filter in many cases. In such cases, the DC voltage is separately supplied to the IC in some types.
Usually, it is necessary to provide a dedicated circuit for supplying the DC voltage between the stacked dielectric filter and the IC. However, in the present invention, the balanced signal, in which the received signal component is superimposed on the DC voltage, is outputted. Therefore, it is unnecessary to connect the dedicated circuit. Accordingly, it is possible to miniaturize the circuit system including the stacked dielectric filter and the IC.
It is preferable that the second and third strip lines are arranged in linear symmetry about a center of a line by which a line segment for connecting the plurality of balanced input/output terminals is equally divided into two, and respective physical lengths of the second and third strip lines are substantially identical with each other. Accordingly, it is possible to obtain the good balance for the input/output characteristics of the respective balanced input/output terminals.
In the present invention, a width of a first portion of the first strip line corresponding to the second strip line, a length of the first portion, a width of a second portion of the first strip line corresponding to the third strip line, a length of the second portion, a width of the second strip line, an electrically effective length of the second strip line, a width of the third strip line, an electrically effective length of the third strip line, and a dielectric constant of the dielectric layer disposed between the first strip line and the second and third strip lines are appropriately changed. By doing so, it is possible to easily establish an output impedance, level balance, and phase balance of the unbalanced-balanced converting section.
Usually, the output impedance of the unbalanced-balanced converting section is twice the input impedance of the unbalanced-balanced converting section. For example, when the input impedance of the unbalanced-balanced converting section is 50xcexa9, the output impedance is 100xcexa9. However, for example, when the impedance, which is required to effect the matching to the IC to be connected to the unbalanced-balanced converting section, is 50xcexa9, then the impedance matching is not satisfied, and an additional circuit is required to effect the impedance matching.
However, in the present invention, even when the input impedance of the unbalanced-balanced converting section is 50xcexa9, the output impedance of the unbalanced-balanced converting section can be easily matched to the input impedance of the IC by appropriately setting the various parameters described above.
Alternatively, the input impedance of the unbalanced-balanced converting section may have a value other than 50xcexa9. For example, when the input impedance is 25xcexa9, the output impedance of the unbalanced-balanced converting section can be 50xcexa9. In the above example, it is possible to satisfy the impedance matching with respect to the IC without separately inserting any impedance-matching circuit, helping the size of the circuit system including the stacked dielectric filter and the IC to be reduced.
Alternatively, the unbalanced-balanced converting section may comprise a first strip line which is formed on a first principal surface of the dielectric layer and which has a first end constituting an unbalanced input/output section; a second strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to one balanced input/output terminal, and which is connected to a ground electrode at an arbitrary position on the line; a third strip line which is formed on a first principal surface of the dielectric layer and which has a first end connected to a second end of the first strip line; and a fourth strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to the other balanced input/output terminal, and which is connected to the ground electrode at an arbitrary position on the line.
In this arrangement, planes on which input/output terminals of the filter section are formed and respective planes on which the first to fourth strip lines of the unbalanced-balanced converting section are formed can be parallel to one another. Accordingly, the input/output terminals of the filter section and the strip lines are arranged away from each other. Therefore, it is possible to eliminate any unnecessary interference between the input/output terminals of the filter section and the strip lines of the unbalanced-balanced converting section. Thus, it is possible to improve the characteristics.
The stacked dielectric filter may further comprise an inner layer ground electrode connected to the ground electrode, the inner layer ground electrode being formed between the dielectric layer on which the second strip line is formed and the dielectric layer on which the third strip line is formed, wherein the second strip line is connected to the inner layer ground electrode at an arbitrary position on the second strip line. In this arrangement, one coupling line based on the first strip line and the second strip line is separated from the other coupling line based on the third strip line and the fourth strip line by the second inner layer ground electrode. Therefore, it is possible to suppress any interference between the coupling lines, and it is possible to obtain the good balance of the input/output characteristics of the unbalanced-balanced converting section.
When a DC electrode, which is connected to a DC power source, is formed on a surface of the dielectric substrate, the unbalanced-balanced converting section may comprise a first strip line which is formed on a first principal surface of the dielectric layer and which has a first end constituting an unbalanced input/output section; a second strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to one balanced input/output terminal, and which is connected to the DC electrode at an arbitrary position on the line; a third strip line which is formed on a first principal surface of the dielectric layer and which has a first end connected to a second end of the first strip line; and a fourth strip line which is formed on a first principal surface of the dielectric layer, which has a first end connected to the other balanced input/output terminal, and which is connected to the DC electrode at an arbitrary position on the line.
In this arrangement, the stacked dielectric filter may further comprise an inner layer ground electrode which is provided in the dielectric substrate and which is connected to a ground electrode, wherein the second and fourth strip lines are connected to the DC electrode at respective arbitrary positions on the second and fourth strip lines through via-holes respectively beyond the inner layer ground electrode. Alternatively, the stacked dielectric filter may further comprise an inner layer DC electrode which is provided in the dielectric substrate and which is connected to the DC electrode, wherein the second and fourth strip lines are connected to the inner layer DC electrode at respective arbitrary positions on the second and fourth strip lines through the via-holes respectively.
Further, in the present invention, a width of the first strip line, a length of the first strip line, a width of the second strip line, an electrically effective length of the second strip line, a width of the third strip line, a length of the third strip line, a width of the fourth strip line, an electrically effective length of the fourth strip line, and a dielectric constant or dielectric constants of one or more of the dielectric layers disposed in a region ranging from the first strip line to the fourth strip line are appropriately determined. Accordingly, it is possible to easily determine an output impedance, level balance, and phase balance of the unbalanced-balanced converting section.
In this arrangement, an input impedance of the unbalanced-balanced converting section may have a value other than 50xcexa9.
In the present invention, a coupling-adjusting electrode for adjusting a coupling degree for the plurality of resonators is formed at a position separated from the connecting section with the resonators interposed therebetween. In this arrangement, if the coupling-adjusting electrode is formed near the connecting section, any stray coupling may be generated between the coupling-adjusting electrode and the connecting section (or the connecting electrode when the connecting section has the connecting electrode connected to the filter section via the capacitor), and it is impossible to eliminate the unnecessary matching. For this reason, it is preferable that the coupling-adjusting electrode is formed at the position separated from the connecting section with the resonators interposed therebetween.
When the resonators are composed of a plurality of resonant electrodes arranged in a stacking direction, the coupling-adjusting electrode may be formed on a first principal surface of one dielectric layer of one or more of the dielectric layers arranged between the resonant electrodes.
In the present invention, the plurality of resonators of the filter section may have different resonance frequencies respectively, and an apparent reactance element may be equivalently connected to an output side of the unbalanced-balanced balanced converting section. Accordingly, when an IC is connected to the unbalanced-balanced converting section, the impedance matching between the unbalanced-balanced converting section and the IC can be realized without inserting any additional matching circuit. Thus, the size of the circuit system including the stacked dielectric filter and the IC can be compact.
As described above, the stacked dielectric filter according to the present invention provides the following effects.
(1) It is possible to effectively realize the miniaturization while realizing the balanced input/output taking the connection of the high frequency amplifying circuit or the like into consideration.
(2) When the IC is connected to the unbalanced-balanced converting section, it is unnecessary to separately insert the circuit for connecting the DC power source to the IC. It is possible to reduce the number of parts, suppress the insertion loss, and miniaturize the size of the electronic devices including the IC.
(3) When the IC is connected to the unbalanced-balanced converting section, it is unnecessary to insert the circuit for matching the impedance between the unbalanced-balanced converting section and IC. It is possible to reduce the number of parts, suppress the insertion loss, and miniaturize the size of the electronic devices including the IC.
(4) It is possible to increase the degree of flexibility of the design.
(5) It is possible to reduce the electrode area in the filter section, and it is possible to suppress the stray coupling in the unbalanced-balanced converting section.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.